Short-circuit MIG welding

Abstract

A method and apparatus for short-circuit MIG welding is described. The apparatus comprises a power supply electrically connected with electrode wire and a workpiece in use; and electrode wire feed means. Monitoring means is provided for monitoring the ratio (M) of one of the mean and successive integral of the arc duration to the corresponding one of the mean and the successive integral of the short-circuit duration. The welding process can be monitored by monitoring the ratio (M).

I claim: 
     
       1. In a method of short-circuit MIG welding in which electrode wire and a workpiece in a welding circuit are moved relatively to one another and in which periods of arcing and short-circuiting successively occur between the electrode wire and the workpiece the improvement comprising monitoring the ratio of the mean of the arc duration to the mean of the short-circuit duration. 
     
     
       2. A method according to claim 1, wherein said ratio is determined over between four and twelve successive short-circuit cycles. 
     
     
       3. A method according to claim 1, further comprising maintaining said monitored ratio substantially constant by adjusting one or more of the open circuit voltage, the effective resistance of the welding circuit, and the average wire feed speed. 
     
     
       4. A method according to claim 3, wherein one or both of said open circuit voltage and said wire feed speed are additionally oscillated about respective mean values to control the frequency of short-circuiting. 
     
     
       5. A method according to claim 3, wherein said open circuit voltage and said wire feed speed are modulated to obtain a preselected mark space ratio. 
     
     
       6. A method according to claim 3, wherein said open circuit voltage or said wire feed speed is modulated to obtain a preselected mark space ratio. 
     
     
       7. In a method of short-circuit MIG welding in which electrode wire and a workpiece in a welding circuit are moved relatively to one another, and in which periods of arcing and short-circuiting successively occur between the electrode wire and the workpiece, the improvement comprising monitoring the ratio of the successive integral of the arc duration to the successive integral of the short-circuit duration. 
     
     
       8. A method according to claim 7, wherein said ratio is determined over between four and twelve successive short-circuit cycles. 
     
     
       9. A method according to claim 7, further comprising maintaining said monitored ratio substantially constant by adjusting one or more of the open circuit voltage, the effective resistance of the welding circuit, and the average wire feed speed. 
     
     
       10. A method according to claim 9, wherein one or both of said open circuit voltage and said wire feed speed are additionally oscillated about respective mean values to control the frequency of short-circuiting. 
     
     
       11. A method according to claim 9, wherein said open circuit voltage and said wire feed speed are modulated to obtain a preselected mark space ratio. 
     
     
       12. A method according to claim 9, wherein said open circuit voltage or said wire feed speed is modulated to obtain a preselected mark space ratio. 
     
     
       13. Short-circuit MIG welding apparatus comprising a power supply adapted to be electrically connected in a welding circuit with electrode wire and a workpiece; and electrode wire feed means, wherein the apparatus further includes means for monitorng the ratio of the mean of the arc duration to the mean of the short-circuit duration. 
     
     
       14. Short-circuit MIG welding apparatus according to claim 13, wherein said monitoring means includes a capacitor which is adapted to be charged as a function of said mean short-circuit duration; and indicating means for providing an indication of the charge stored by said capacitor. 
     
     
       15. Short-circuit MIG welding apparatus according to claim 14, further comprising control means adapted to adjust one or more of the effective emf of said power supply, the effective resistance of said welding circuit and the average wire feed speed in accordance with a signal supplied by said monitoring means representative of said stored charge. 
     
     
       16. Short-circuit MIG welding apparatus according to claim 13, wherein said monitoring means includes means for determining the mean of the arc duration and the mean of the short-circuit duration and means for determining the ratio therebetween, and means for providing an indication of said determined ratio. 
     
     
       17. Short-circuit MIG welding apparatus according to claim 16, further comprising control means adapted to adjust one or more of the effective emf of said power supply, the effective resistance of said welding circuit and the average wire feed speed in accordance with a signal supplied by said monitoring means representative of said determined ratio. 
     
     
       18. Short-circuit MIG welding apparatus according to claim 13, further comprising a switched impedance in said welding circuit adapted to modulate the effective emf of said power supply. 
     
     
       19. Short-circuit MIG welding apparatus comprising a power supply adapted to be electrically connected in a welding circuit with electrode wire and a workpiece; and electrode wire feed means, wherein the apparatus further includes means for monitoring the ratio of the successive integral of the arc duration to the successive integral of the short-circuit duration. 
     
     
       20. Short-circuit MIG welding apparatus according to claim 15, wherein said monitoring means includes means for determining the successive integral of the arc duration and the successive integral of the short-circuit duration and means for determining the ratio therebetween, and means for providing an indication of said determined ratio. 
     
     
       21. Short-circuit MIG welding apparatus according to claim 20, further comprising control means adapted to adjust one or more of the effective emf of said power supply, the effective resistance of the said welding circuit, and the average wire feed speed in accordance with a signal supplied by said monitoring means representative of said determined ratio. 
     
     
       22. Short-circuit MIG welding apparatus according to claim 19, further comprising a switched impedance in said welding circuit adapted to modulate the effective emf of said power supply.